This invention relates to waste treatment systems, and in particular, to a single-unit, single-zone bioreactor for the combined removal of organics and nitrogen while operating in both down-flow and up-flow modes with intermittent aeration to the filter.
The presence of nitrogen compounds in lakes, rivers and other water bodies promote unwanted growth of algae and other aquatic plants than consume dissolved oxygen. Consequently, there is a need to reduce nitrogen compounds in wastewater prior to discharge of the wastewater.
A number of processes and apparatus have been proposed for the nitrification and denitrification of wastewater containing nitrogen compounds. Generally, in such systems, wastewater containing nitrogen compounds, such as ammonia and organic nitrogen compounds, is passed through a reactor vessel under aerobic conditions and then passed through another reactor vessel under anoxic conditions to denitrify the nitrified wastewater. Nitrogen gas formed during denitrification is released to the atmosphere while the treated wastewater having a reduced level of nitrogen compounds is returned to the ground or receiving stream. Typically, such systems also utilize a settling tank or clarification zone after the wastewater has been biologically treated.
Accordingly, there is a need for a process and apparatus that reduces nitrogen compounds from wastewater to an environmentally acceptable level and is relatively simple to operate and maintain. One such process is based on a submerged attached growth bioreactor.
There are two primary advantages obtained in using a submerged attached growth bioreactor. A submerged attached growth bioreactor has a small volume requirement and eliminates the need for downstream clarification. Media used in a submerged attached growth bioreactor has a high specific surface area. This allows a high biomass concentration to be maintained within the reactor and, therefore, a short hydraulic time (HRT). The short HRT results in a relatively smaller volume bioreactor requirement to treat a given waste strength. In addition, the media provides physical filtration thereby avoiding the need for solids separation after the biological treatment process. Different configurations of submerged attached growth bioreactors have been conceived and advances in understanding of these systems have been made.